A new one-dimensional platinum mixed-valence complex with nonhalogen bridging ligands, namely catena-poly[[[bis(ethane-1,2-diamine-κ2N,N′)platinum(II)]-μ-thiocyanato-κ2S:S-[bis(ethane-1,2-diamine-κ2N,N′)platinum(IV)]-μ-thiocyanato-κ2S:S] tetrakis(perchlorate)], {[Pt2(SCN)2(C2H8N2)4](ClO4)4}n, has been isolated. The PtII and PtIV atoms are located on centres of inversion and are stacked alternately, linked by the S atoms of the thiocyanate ligands, forming an infinite one-dimensional chain. The PtIV—S and PtII...S distances are 2.3933 (10) and 3.4705 (10) Å, respectively, and the PtIV—S...PtII angle is 171.97 (4)°. The introduction of nonhalogen atoms as bridging ligands in this complex extends the chemical modifications possible for controlling the amplitude of the charge-density wave (CDW) state in one-dimensional mixed-valence complexes. The structure of a discrete PtIV thiocyanate compound, bis(ethane-1,2-diamine-κ2N,N′)bis(thiocyanato-κS)platinum(IV) bis(perchlorate) 1.5-hydrate, [Pt(SCN)2(C4H8N2)2](ClO4)2·1.5H2O, has monoclinic (C2) symmetry. Two S-bound thiocyanate ligands are located in trans positions, with an S—Pt—S angle of 177.56 (3)°.